A variational perturbation theory of inhomogeneous liquid metals: applications to the calculation of surface properties

Abstract

Assuming that the electron–ion interaction can be treated by a weak pseudopotential, we develop a theory for calculating the thermodynamic properties of inhomogeneous liquid metals. We first derive an effective Hamiltonian for the classical ion system using an improved perturbation expansion in the pseudopotential, in which an averaged ionic potential is effectively included in the unperturbed electron system. The Helmholtz free energy is then calculated using the variational method based on the Gibbs – Bogoliubov inequality. The results of this formulation are compared with the previous theories, and the approximations involved in these theories are critically analyzed. Finally, the formulation is applied to liquid-metal surfaces and the surface tension is calculated. In these applications, we use the classical one-component plasma as the reference system of the variational method.